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Phase-change technology has been widely used in rewritable disks for optical recording applications. Recently, it has also received attention as a candidate for future high-storage-density nonvolatile random access memory, due to its much longer cycle life (∼1013) and fast data access time (∼100 ns) compared with the existing flash memory technology. In this article, we present thermal conductivity data and models for phase-change GeSbTe material that would be helpful in performance optimization and improvement in the reliability of phase change–based data storage devices and systems. We present thermal conductivity data for a 40-nm-thick Ge2Sb2Te5 phase-change layer in both amorphous and crystalline states using electrical resistance joule heating and thermometry techniques. The limits of lattice and electronic thermal conductivities are investigated to determine their relative contributions to the total thermal conductivity as a function of tellurium concentration, crystalline structures, and temperature.

The industry trend toward reduced feature size and faster operating speed has generated demand for higher powered devices. The increased power and reduced overall area creates higher thermal loads for the package. This has led to the need for new thermal materials with high thermal conductivity. High-performance thermal interface greases, gels, and adhesives significantly improve the transmission of the heat generated by the high power densities out of the system. Thermal greases generally have higher thermal conductivity than gels or adhesives with similar fillers. Unfortunately, greases typically pump out and separate during use. Additionally, some applications that require higher thermal conductivity materials cannot go through a cure profile normally used for non-grease thermal interface materials (TIMs). Use of integrated heat spreaders avoids some of the processing restrictions placed on board-level thermal solutions, but many applications -- particularly in mobile electronics -- have little space or have significant weight constraints that interfere with the use of a built-in heat spreader. A new 4 W/mK silicone thermal grease with dramatic property improvements has been developed with significant resistance to in-package bleed-out or pump-out, eliminating the reliability problem most commonly encountered with traditional thermal greases.

Increase of power densities has become the primary constraint for semiconductor industry to sustain the Moore’s law for microprocessor evolution. Further development of packaging technology and advanced thermal interface materials (TIMs) requires both maximization of the total thermal throughput of the system and mitigation of the thermal impact from non-uniformly distributed hotspots. Therefore, thermal characterization techniques capable of resolving partial thermal resistances at the component level have received increased emphasis in development of advanced packaging technologies. This work develops a practical method for thermal characterization of IC packages using the frequency-domain measurement technique. It is well suited for investigation of package thermal performance during various application-specific tests in field conditions, as well as a tool for development of TIM and optimization of packaging process. Both steady-state and dynamic thermal characterizations of the IC packages can be achieved using this technique. Various applications, such as thermal structure function measurement, silicon die hot-spot detection, and in-situ thermal/mechanical characterization of TIMs are discussed.Copyright © 2009 by ASME

In this paper, a thermal analysis of thermoelectric coolers (TECs) is conducted for processors based on TEC module parameters. Two sets of analytical solutions for TECs in system constraints are derived for the junction temperature Tj at a fixed power Qc, and for Qc at fixed Tj, respectively. The major advantage of the present models lies in the fact that the solutions can be obtained based on the module parameters without prior knowledge of pellet details and iterative solution procedure, as often reported in literature. Two cooling scenarios, the processor test and the processor cooling under end-user conditions, are analyzed based on the present analysis models for two commercial TECs with high power capacities. Results show that significant thermal enhancements are achievable based on optimized current and power dissipation. The validation is also conducted through experimental measurements and comparison with previous iterative solutions.

Phase-change technology has been widely used in rewritable disks for optical recording applications. Recently, it has also received attention as a candidate for future high storage density non-volatile random access memory, due to its much longer cycle life (∼1013 ) and fast data access time (∼100ns) compared with the existing Flash memory technology. In this paper, we present thermal conductivity data and models for phase-change GeSbTe material that would be helpful in performance optimization and improvement in the reliability (i.e., enhancement of data rate, cyclability, control of mark-edge jitter) of phase-change-based data storage devices and systems. We perform the thermal characterization of Ge4 Sb1 Te5 and Ge2 Sb2 Te5 phase-change materials for the application of optical recording and phase-change memory cell using the techniques of thermoreflectance and electrical resistance thermometry. The limits of lattice and electronic thermal conductivities are investigated to determine their relative contributions as a function of tellurium concentration at different crystalline structures.Copyright © 2007 by ASME

The discovery of the giant magnetoresistance effect in metallic multilayers and alloys has led to extensive theoretical and experimental investigations of this effect for the past few decades. Recently, we discovered that Cu/CoFe giant magneto-resistance layers exhibit a giant magnetothermal resistance effect (GMTR), in which the thermal conductivity shows a “giant” change under a magnetic field. In the present study, we adopted the Fuchs-Sondheimer extension of the semiclassical Boltzmann theory to predict the in-plane giant magneto-resistance (GMR) and giant magnetothermal resistance (GMTR) ratios in the Cu/CoFe multilayer structure. The present model has been implemented in an attempt to explain the measured differences in the giant magnetoresistance and giant magnetothermal resistance ratios, which have previously been attributed to the different mechanisms for charge and heat transport in the Cu/CoFe multilayer structure.Copyright © 2007 by ASME

This paper presents the experimental and theoretical study on the effects of electron scattering at grain and boundaries on the reduction of effective thermal conductivity. The present study measures the electrical resistivity and lateral thermal conductivity of thin copper layers of thicknesses 50 and 144 nm at temperatures between 40 and 400 K, using Joule heating and electrical-resistance thermometry in suspended micro fabricated structures. A fitting model including the size effect and grain boundary scattering is used to model the thermal conductivity and electrical resistivity of thin copper film simultaneously and is consistent with the experimental results. The thermal conductivity of the 50 nm thick copper layer is ~150 W m-1 K-1, which is much smaller than the bulk value (~400 W m-1 K-1) at room temperature. The experimental and modeling data are essential to address performance and reliability issues for future device and interconnect technologies

When crystalline solids are confined to the nanometer range, phonon transport within them can be significantly altered due to various effects, namely (i) increased boundary scattering; (ii) changes in phonon dispersion relation; and (iii) quantization of phonon transport. For example, theoretical studies (e.g., Chung et al., 2000) have suggested that, as the diameter of a silicon nanowire (NW) becomes smaller than 20 nm, the phonon dispersion relation, and therefore its density of states, could be modified due to phonon confinement. This in turn impacts the phonon group velocities and scattering rates that can further reduce the thermal conductivity of confined structures.

The performance and reliability of GMR heads are influenced by the level of temperature rise, which may occur in the device during the normal operation or during an electrostatic discharge (ESD) event. However, the reliable electro-thermal modeling of the GMR sensor to predict the temperature rise, demands an accurate knowledge of the thermal properties of its constituent materials such as Al2 O3 passivation and GMR layers. The lateral thermal conductivity of the GMR layer, which has not been measured previously, can largely influence the maximum temperature rise in the GMR sensor. The present effort will be directed at thermal characterization of the CoFe/Cu multilayer structures made of extremely thin periodic layers, using steady-state and frequency domain heating and thermometry in suspended bridges. The measurements are performed on several suspended structures with the lengths and widths in the range of 250 to 500 μm and 16 to 20 μm, respectively.Copyright © 2003 by ASME

With the further miniaturization of the GMR heads, the electrostatic discharge (ESD) failure has become the primary reliability issue in manufacturing of these sensors. The Joule heating effect during the ESD events result in both thermal and magnetic damages in GMR heads. In this paper, the thermal response of the GMR read head to the excessive current/voltage during an ESD event is investigated numerically using a 3-D finite element analysis. Unlike the previous studies, the thermal properties of the GMR and Al2 O3 gap layers used in the simulation are the experimentally measured values. The temperature-rise in GMR heads under human-body-model (HBM) source current is obtained for a range of GMR dimensions and thermal properties of its constituent materials. The simulation results show that temperature in the GMR element sharply increases as the GMR dimensions are reduced, indicating the future GMR heads are more susceptible to the ESD damages. In addition, thermal properties of the GMR and gap materials play key roles in accurate prediction of the temperature field in GMR head during ESD events.Copyright © 2003 by ASME

Advanced thin-film growth technology has made it possible to arrange different materials at the atomic level and to fabricate thin-film structures (e.g., GMR) with strong quantum effects. GMR devices appear in two important areas of storage technology: GMR sensors for magnetic read heads, and Magnetic Random Access Memory (MRAM). The former is a well-established commercial technology, in which nanoscale thermal transport is related to reliability, through electrostatic discharge (ESD) events as well as performance. In MRAM, the nanoscale thermal transport limits device ultimate performance, but may also present an opportunity for assisted switching. The thermal transport properties of these thin periodic layers play an important role in design, performance and reliability of these devices, which are fundamentally different from their bulk counterparts [1,2].Copyright © 2002 by ASME